Southborough is an affluent town in Worcester County, Massachusetts, United States. It incorporates the smaller villages of Cordaville, Fayville, and Southville. Its name is often informally shortened to Southboro, a usage seen on many area signs and maps, though officially rejected by town ordinance. Its population was 9,767 at the 2010 census, in nearly 3,000 households. First settled in 1660, land use now is primarily residential, with substantial open space. A tenth of the town's area is flooded by the Sudbury Reservoir. Light industrial land use is concentrated along main roads, primarily Massachusetts Route 9, and there are several small business districts in the villages and along Route 9. Southborough was named Number 31 in the nation on CNN Money's "100 Best Places to Live" in 2009.

According to the United States Census Bureau, the town has a total area of 15.7 square miles (41 km2), of which 14.1 square miles (37 km2) is land and 1.5 square miles (3.9 km2), or 9.64%, is water. Southborough is located in eastern Massachusetts, bordered by Hopkinton on the south, Framingham and Ashland on the east, Westborough and Northborough on the west, and Marlborough on the north.

By the census of 2010, the population had reached 9,767. As of the census of 2000, there were 8,781 people, 2,952 households, and 2,426 families residing in the town. The population density was 620.7 inhabitants per square mile (239.7 /km2). There were 2,997 housing units at an average density of 211.8 per square mile (81.8 /km2).